Expendable-Mold Processes Using Single-Use Patterns

Investment casting
One of the oldest casting methods
Products such as rocket components, and jet engine turbine blades
Complex shapes
Most materials can be cast

Investment Casting

Sequential steps for investment casting

Produce a master pattern

Produce a master die

Produce wax patterns

Assemble the wax patterns onto a common wax sprue

Coat the tree with a thin layer of investment material

Form additional investment around the coated cluster

Allow the investment to harden

Remove the wax pattern from the mold by melting or dissolving

Heat the mold

Pour the molten metal

Remove the solidified casting from the mold

Advantages and Disadvantages of Investment Casting

Disadvantages

Complex process

Can be costly

Advantages

Complex shapes can be cast

Thin sections can be cast

Machining can be eliminated or reduced

Evaporative pattern processes

Pattern is made of polystyrene or polymethylmethacrylate
Pattern remains in the mold until the molten metal melts away the pattern
If small quantities are required, patterns may be cut by hand
Material is lightweight
Evaporative Patterns
Metal mold or die is used to mass-produce the evaporative patterns
For multiple and complex shapes, patterns can be divided into segments or slices
Assembled by hot-melt gluing
Full-mold process
Green sand is compacted around the pattern and gating system
Lost Foam Process
Advantages of the Full-Mold and Lost-Foam Process
Sand can be reused
Castings of almost any size
Both ferrous and nonferrous metals
No draft is required
Complex patterns
Smooth surface finish
Absence of parting lines